Commercial Superphosphate Research Articles

Enhancement of the Plant-Accessible Phosphate Fraction in Sewage Sludge Ashes by Na+ or K+ Addition Prior to Combustion.

With the aim of transforming sewage sludge into a P-fertiliser material in a single combustion step, the chemical processes underlying sewage sludge combustion were analysed using powder X-ray diffraction (P-XRD), infrared spectroscopy (IR), thermogravimetric (TGA) as well as elemental analyses (EA). In addition to the combustion of sewage sludge on its own ("mono-combustion"), additions of different additives prior to the combustion step were also carried out. Based on the very positive effects of the additives sodium and potassium carbonate on the obtained ashes concerning their phosphate solubilities in neutral ammonium citrate (NAC) solution, sewage sludge combustions after additions of Na2CO3 or K2CO3 were investigated in detail. We found that these additions altered the main phosphate-containing product found in the ashes from whitlockite (Ca9(Mg,Fe)(PO3OH)(PO4)6), a hardly plant-accessible species, to other phosphate containing compounds such as buchwaldite (CaNaPO4), which is known for a long time as a very good P‑source for plants. Consecutive greenhouse experiments with maize (Zea mays L.) as test plant confirmed the results of the chemical analyses and demonstrated that Na- or K-ashes obtained from a "co-combustion" of sewage sludge mixed with alkali carbonates exhibit relative P-fertilising efficiencies of up to ~80% in comparison to commercial superphosphate.

Phosphorus Fertilizers From Sewage Sludge Ash and Animal Blood Have No Effect on Earthworms

Soil invertebrates are crucial for agroecosystem functioning yet sensitive to agricultural practices, including fertilization. Considering the postulates of circular phosphorus economy, the use of fertilizers from secondary raw materials is likely to return and increase and may even become obligatory. The effects of recycled fertilizers on soil fauna communities, however, remain poorly understood. In this paper, the effect of phosphorus fertilizer (RecF) and biofertilizer (RecB) from sewage sludge ash and dried animal (porcine) blood on earthworm’s occurrence in soil is discussed. RecB is RecF activated by phosphorus-solubilizing bacteria, Bacillus megaterium. Waste-based fertilizers were assessed in field experiments against commercial superphosphate and no P fertilization. Three levels of P doses were established (17.6, 26.4, and 35.2 kg P ha−1). Earthworms were collected after the test crop harvest (spring or winter wheat). In the experiments two earthworm species, Aporrectodea caliginosa and Aporrectodea rosea, were identified. A large proportion of juvenile individuals were recorded in 2017. The recycled fertilizers used in the experiments used in recommended doses, similarly to superphosphate, did not alter the density, biomass, species composition, and structure of earthworms. Further long-term field research is recommended.

Removal of sewage phosphorus by adsorption and mineral precipitation, with recovery as a fertilizing soil amendment.

Clear sand adsorbs 15-35% total phosphorus (P) from septic tank effluent, but P is mobilized when low-P effluent is applied. Amorphous P compounds formed by alkali aluminate chemical addition may also be subject to leaching. Crystalline mineralization is the desired end effect that isolates P thoroughly from the water resource. Using new low-energy iron electrochemistry (EC-P process), dissolved ferrous iron reacts with sewage phosphate ions (PO4) and precipitates onto filtration medium as vivianite [Fe3(PO4)2·8H2O], as identified by scanning electron microscopy and X-ray diffraction and predicted from Eh-pH-aHPO42- phase relations. Removal rates of 90-99% in sand, soil and synthetic foam filters are obtained. The precipitation of vivianite demonstrates that P can be immobilized quickly and without intermediary adsorption phases, as with Fe-rich soils. Vitreous silicate material (VSM) or rockwool that traps and precipitates mineral P after EC-P treatment was investigated as a means of P reuse as a fertilizing soil amendment. Comparative soil leaching and growth studies using corn plants demonstrate that the VSM alone reduces P losses from soils, and that VSM which has received EC-P effluent is equivalent to or better than commercial superphosphate fertilizer.

Lead Bioaccessibility in Soil and Mine Wastes After Immobilization with Phosphate

The immobilization of lead by the reaction with phosphate bearing materials is a promising remediation method for contaminated soils. Low soluble neo-formed lead-phosphate phases similar to chloropyromorphite [Pb5(PO4)3Cl], can control availability and mobility of lead in the environment, and consequently reduce human exposure, if soils are the main contamination pathway. We used three phosphate source materials [NaH2(PO4)3, commercial superphosphate and phosphate rock] to study lead immobilization in soil and mining waste samples. Products were examined after 1, 3 and 6 months of contact. The samples are from a contaminated area by former Pb mining and smelting activities, in southeastern Brazil, where epidemiological studies showed high lead blood levels in local population. The PBET (physiological based extraction test) bioaccessibility test was used to measure changes in the amount of soluble lead after sample treatment. Results show that the most efficient phosphate source was NaH2(PO4)3, which reduced lead solubility to 92% in acidic gastric conditions after the first month of contact. Superphosphate and phosphate rock also diminished Pb solubility, but the effect was more time dependent. None specific Pb–phosphate phases could be identified by XRD in whole treated samples, but the Pb–Ca–P elemental associations, observed on SEM images and EDS spectra of portions of the samples, combined with the reduced solubility, indicate that more insoluble lead phases were formed after the treatment. Based in these results, the in site phosphate application on soils to induce lead immobilization should be considered as a possible alternative to reduce human exposure at the area.

Plant Availability of Phosphorus in Four Superphosphate Fertilizers Varying in Water‐Insoluble Phosphate Compounds

There is concern that the use of lower quality phosphate rock can result in elevated amounts of Fe–Al–P water‐insoluble compounds in fertilizers and, consequently, low agronomic effectiveness. Therefore, studies were conducted to evaluate the effect of some of these compounds on plant growth. Four commercial superphosphates varying in chemical composition (two single and two triple superphosphates) were selected for the study. Fertilizer impurities were collected as water‐insoluble residues by washing each P source with deionized water. A modal analysis, based primarily on elemental chemical analysis and x‐ray diffractometry, was used to estimate the chemical composition of each P source. Water‐soluble monocalcium phosphate (MCP) and the water‐leached fertilizer residues were prepared to give a range of fertilizers in terms of water‐soluble phosphorus (WSP) (0–100% of the available P as MCP). The water‐leached fractions, MCP, and the mixtures of MCP with water‐leached fractions were applied to supply 40 mg available P kg−1 to a thermic Rhodic Kanhapludult with pH values of 5.2 ± 0.05 (unlimed) and 6.4 ± 0.08 (limed). Wheat (Triticum aestivum L.) grown in a greenhouse for 101 d served as the test crop. The requirement for WSP was source and pH dependent. At a soil pH of 5.2, the fertilizers required 73 to 95% WSP to reach the maximum dry‐matter yield, while they required 60 to 86% WSP at pH 6.4. To reach 90% of the maximum yield, all superphosphate fertilizers required <50% WSP. These results show that it is not always necessary to have high water solubility as required by legislation in many countries.

Plant availability of p in commercial superphosphate fertilizers

Abstract The quality of phosphate rock (PR) is declining and the use of lower quality PR results In lower water‐soluble and higher citrate‐soluble P in the fertilizer product. A greenhouse study was conducted to evaluate the plant availability of P in commercial superphosphate fertilizers having various levels of water‐soluble P. Seven commercial fertilizers, Including 6 granular concentrated superphosphates and one normal superphosphate, were evaluated. Reagent grade monocalcium phosphate served as a control. The fertilizers were manufactured from PR deposits located in the United States (Florida, Idaho and North Carolina) and Morocco. Water‐soluble P ranged from 77 to 92 X of the total fertilizer P. Citrate‐soluble, water‐insoluble P ranged from 7 to 20 % of the total fertilizer P. Four of the 5 American fertilizers had a lower percentage of water‐soluble P as compared to the concentrated superphosphate from Morocco. Fertilizers manufactured from U.S. phosphate deposits contained an average of 6 times m...

Dissolution rates of ionic solids. Part 2.—Calcium bis(dihydrogen phosphate) monohydrate + anhydrite (calcium sulphate)

The dissolution rate of commercial superphosphate fertiliser was studied at 25, 35 and 45°C using a rotating disc of the solid material. The kinetics were followed by means of a calcium ion-selective electrode and spectrophotometric analyses. The initial process was observed to consist predominately of calcium bis(dihydrogen phosphate) monohydrate dissolution and was transport controlled with an apparent activation energy of 13 ± 3 kJ mol–1. Thereafter diffusion of dissolved monocalcium bis(dihydrogen phosphate) monohydrate through a porous layer of increasing thickness determined the rate of dissolution.

Iron and aluminum compounds in commercial superphosphates

Iron and aluminum compounds in commercial superphosphates

Pasture responses to traces of zinc in phosphate fertilizers

The effect of zinc present as a contaminant in commercial superphosphate was compared with the zinc in zinc sulphate (ZnSO4.7H2O) in its effect on subterranean clover grown on a deficient light soil (Kojonup sand) in the field. A dressing of 55 grams of zinc an acre, applied as a contaminant in superphosphate, increased the yield of subterranean clover in the pear of application from 2300 to 3200 lb of dry matter an acre. The total uptake of zinc in the tops was increased from 11 to 19 grams of zinc an acre. The proportion of the contaminant zinc absorbed from superphosphate was at least equal to that absorbed from a dressing of ZnSO4.7H2O. These results are discussed in relation to the zinc contents of superphosphate and of various compounds used in phosphatic fertilizers. The evidence indicates that the amount of zinc contaminant applied in the present experiment could be contained in dressings of even less than 2 cwt an acre of superphosphate.